Fitting Algorithm for Recruiting of Neural Targets in a Spinal Cord Stimulator System

ABSTRACT

A fitting algorithm for a spinal cord stimulator is disclosed, which is preferably implemented in a clinician programmer having a graphical user interface. In one example, coupling parameters indicative of coupling to neural structures are determined for each electrode in an implanted electrode array. The user interface associates different pole configurations with different anatomical targets and with different measurement techniques (subjective or objective) to gauge the effectiveness of the pole configuration at different positions in the electrode array. The pole configuration, perhaps as modified by the coupling parameters, is then steered in the array, and effectiveness is measured along with a paresthesia threshold at each position. Using at least this data, the fitting algorithm can determine one or more candidate positions in the electrode array at which a therapeutic stimulation program can be centered.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 16/737,663,filed Jan. 8, 2020, which is a non-provisional application of U.S.Provisional Patent Application Ser. No. 62/795,268, filed Jan. 22, 2019.These applications are incorporated herein by reference, and priority isclaimed to them.

FIELD OF THE INVENTION

This application relates to Implantable Medical Devices (IMDs), and morespecifically to techniques for providing stimulation in implantableneurostimulation systems.

INTRODUCTION

Implantable neurostimulator devices are devices that generate anddeliver electrical stimuli to body nerves and tissues for the therapy ofvarious biological disorders, such as pacemakers to treat cardiacarrhythmia, defibrillators to treat cardiac fibrillation, cochlearstimulators to treat deafness, retinal stimulators to treat blindness,muscle stimulators to produce coordinated limb movement, spinal cordstimulators to treat chronic pain, cortical and deep brain stimulatorsto treat motor and psychological disorders, and other neural stimulatorsto treat urinary incontinence, sleep apnea, shoulder subluxation, etc.The description that follows will generally focus on the use of theinvention within a spinal cord stimulation (SCS) system, such as thatdisclosed in U.S. Pat. No. 6,516,227. However, the present invention mayfind applicability with any implantable neurostimulator device system.

An SCS system typically includes an Implantable Pulse Generator (IPG) 10shown in FIG. 1. The IPG 10 includes a biocompatible conductive devicecase 12 that holds the IPG's circuitry and a battery 14 for providingpower for the IPG to function. The IPG 10 is coupled totissue-stimulating electrodes 16 via one or more electrode leads thatform an electrode array 17. For example, one or more percutaneous leads15 can be used having ring-shaped or split-ring electrodes 16 carried ona flexible body 18. In another example, a paddle lead 19 provideselectrodes 16 positioned on one of its generally flat surfaces. Leadwires 20 within the leads are coupled to proximal contacts 21, which areinsertable into lead connectors 22 fixed in a header 23 on the IPG 10,which header can comprise an epoxy for example. Once inserted, theproximal contacts 21 connect to header contacts 24 within the leadconnectors 22, which are in turn coupled by feedthrough pins 25 througha case feedthrough 26 to stimulation circuitry 28 within the case 12,which stimulation circuitry 28 is described below.

In the illustrated IPG 10, there are thirty-two electrodes (E1-E32),split between four percutaneous leads 15, or contained on a singlepaddle lead 19, and thus the header 23 may include a 2×2 array ofeight-electrode lead connectors 22. However, the type and number ofleads, and the number of electrodes, in an IPG is application specificand therefore can vary. The conductive case 12 can also comprise anelectrode (Ec). In a SCS application, the electrode lead(s) aretypically implanted in the spinal column proximate to the dura in apatient's spinal cord, preferably spanning left and right of thepatient's spinal column. The proximal contacts 21 are then tunneledthrough the patient's tissue to a distant location such as the buttockswhere the IPG case 12 is implanted, where they are coupled to the leadconnectors 22. In other IPG examples designed for implantation directlyat a site requiring stimulation, the IPG can be lead-less, havingelectrodes 16 instead appearing on the body of the IPG 10 for contactingthe patient's tissue. The IPG lead(s) can be integrated with andpermanently connected to the IPG 10 in other solutions. The goal of SCStherapy is to provide electrical stimulation from the electrodes 16 toalleviate a patient's symptoms, such as chronic back pain.

IPG 10 can include an antenna 27 a allowing it to communicatebi-directionally with a number of external devices discussedsubsequently. Antenna 27 a as shown comprises a conductive coil withinthe case 12, although the coil antenna 27 a can also appear in theheader 23. When antenna 27 a is configured as a coil, communication withexternal devices preferably occurs using near-field magnetic induction.IPG 10 may also include a Radio-Frequency (RF) antenna 27 b. RF antenna27 b is shown within the header 23, but it may also be within the case12. RF antenna 27 b may comprise a patch, slot, or wire, and may operateas a monopole or dipole. RF antenna 27 b preferably communicates usingfar-field electromagnetic waves, and may operate in accordance with anynumber of known RF communication standards, such as Bluetooth, Zigbee,MICS, and the like.

Stimulation in IPG 10 is typically provided by a sequence of waveforms(e.g., pulses) each of which may include a number of phases such as 30 aand 30 b, as shown in the example of FIG. 2A. Stimulation parameterstypically include amplitude (current A, although a voltage amplitude Vcan also be used); frequency (f); pulse width (PW) of the phases of thewaveform such as 30 a and 30 b; the electrodes 16 selected to providethe stimulation; and the polarity of such selected electrodes, i.e.,whether they act as anodes that source current to the tissue or cathodesthat sink current from the tissue. These and possibly other stimulationparameters taken together comprise a stimulation program that thestimulation circuitry 28 in the IPG 10 can execute to providetherapeutic stimulation to a patient.

In the example of FIG. 2A, electrode E1 has been selected as an anode(during first phase 30 a), and thus sources a positive current ofamplitude +A to the tissue. Electrode E2 has been selected as a cathode(again during first phases 30 a), and thus sinks a correspondingnegative current of amplitude −A from the tissue. This is an example ofbipolar stimulation, in which only lead-based electrodes are used toprovide stimulation to the tissue. However, more than one electrode maybe selected to act as an anode at a given time, and more than oneelectrode may be selected to act as a cathode at a given time. The caseelectrode may also be selected as an anode or cathode along with one ormore lead-based electrodes, in what is known as monopolar stimulation.

IPG 10 as mentioned includes stimulation circuitry 28 to form prescribedstimulation at a patient's tissue. FIG. 3 shows an example ofstimulation circuitry 28, which includes one or more current sources 40_(i) and one or more current sinks 42 _(i). The sources and sinks 40_(i) and 42 _(i) can comprise Digital-to-Analog converters (DACs), andmay be referred to as PDACs 40 _(i) and NDACs 42 _(i) in accordance withthe Positive (sourced, anodic) and Negative (sunk, cathodic) currentsthey respectively issue. In the example shown, a NDAC/PDAC 40 _(i)/42_(i) pair is dedicated (hardwired) to a particular electrode node ei 39.Each electrode node ei 39 is connected to an electrode Ei 16 via aDC-blocking capacitor Ci 38, for the reasons explained below. PDACs 40_(i) and NDACs 42 _(i) can also comprise voltage sources.

Proper control of the PDACs 40 _(i) and NDACs 42 _(i) allows any of theelectrodes 16 and the case electrode Ec 12 to act as anodes or cathodesto create a current through a patient's tissue, R, hopefully with goodtherapeutic effect. In the example shown, and consistent with the firstphase 30 a of FIG. 2A, electrode E1 has been selected as an anodeelectrode to source current I=+A to the tissue R and electrode E2 hasbeen selected as a cathode electrode to sink current I=−A from thetissue R. Thus PDAC 40 ₁ and NDAC 42 ₂ are activated and digitallyprogrammed to produce the desired current, I, with the correct timing(e.g., in accordance with the prescribed frequency f and pulse widthPW). Power for the stimulation circuitry 28 is provided by a compliancevoltage VH, as described in further detail in U.S. Patent ApplicationPublication 2013/0289665.

Other stimulation circuitries 28 can also be used in the IPG 10. In anexample not shown, a switching matrix can intervene between the one ormore PDACs 40 _(i) and the electrode nodes ei 39, and between the one ormore NDACs 42 _(i) and the electrode nodes. Switching matrices allowsone or more of the PDACs or one or more of the NDACs to be connected toone or more electrode nodes at a given time. Various examples ofstimulation circuitries can be found in U.S. Pat. Nos. 6,181,969,8,606,362, 8,620,436, and U.S. Patent Application Publications2018/0071520 and 2019/0083796.

Much of the stimulation circuitry 28 of FIG. 3, including the PDACs 40_(i) and NDACs 42 _(i), the switch matrices (if present), and theelectrode nodes ei 39 can be integrated on one or more ApplicationSpecific Integrated Circuits (ASICs), as described in U.S. PatentApplication Publications 2012/0095529, 2012/0092031, 2012/0095519,2018/0071516, and 2018/0071513, which are incorporated herein byreference in their entireties. As explained in these references, ASIC(s)may also contain other circuitry useful in the IPG 10, such as telemetrycircuitry (for interfacing off chip with telemetry antennas 27 a and/or27 b), circuitry for generating the compliance voltage VH, variousmeasurement circuits, etc.

Also shown in FIG. 3 are DC-blocking capacitors Ci 38 placed in seriesin the electrode current paths between each of the electrode nodes ei 39and the electrodes Ei 16 (including the case electrode Ec 12). TheDC-blocking capacitors 38 act as a safety measure to prevent DC currentinjection into the patient, as could occur for example if there is acircuit fault in the stimulation circuitry 28. The DC-blockingcapacitors 38 are typically provided off-chip (off of the ASIC(s)), andinstead may be provided in or on a circuit board in the IPG 10 used tointegrate its various components, as explained in U.S. PatentApplication Publication 2015/0157861.

Referring again to FIG. 2A, the stimulation waveforms as shown arebiphasic, with each waveform comprising a first phase 30 a followedthereafter by a second phase 30 b of opposite polarity. (Although notshown, an interphase period during which no active current is driven mayintervene between the phases 30 a and 30 b). Both of the phases 30 a and30 b are actively driven by the stimulation circuitry 28 by causingrelevant PDACs 40 _(i) and NDACs 42 _(i) to drive the prescribedcurrents. Biphasic waveforms are useful to actively recover any chargethat might be stored on capacitive elements in the current path, such ason the DC-blocking capacitors 38. Charge recovery is shown withreference to both FIGS. 2A and 2B. During the first phases 30 a, chargewill build up across the DC-blocking capacitors C1 and C2 associatedwith the electrodes E1 and E2 selected to produce the current, givingrise to voltages Vc1 and Vc2. Given the definition of these voltages inFIG. 2B, they are of the same polarity as shown in FIG. 2A. During thesecond phases 30 b, when the polarity of the current is reversed at theselected electrodes E1 and E2, the stored charge on capacitors C1 and C2is recovered, and thus voltages Vc1 and Vc2 return to 0V at the end thesecond phase 30 b.

To recover all charge by the end of the second phase 30 b of eachwaveform (Vc1=Vc2=0V), the first and second phases 30 a and 30 b arecharged balanced at each electrode, with the first phase 30 a providinga charge of +Q (+A*PW) and the second phase 30 b providing a charge of−Q (−A*PW) at electrode E1, and with the first phase 30 a providing acharge of −Q and the second phase 30 b providing a charge of +Q at theelectrode E2. In the example shown, such charge balancing is achieved byusing the same phase width (PW) and the same amplitude (|A|) for each ofthe opposite-polarity phases 30 a and 30 b. However, the phases 30 a and30 b may also be charged balance at each electrode if the product of theamplitude and pulse width of the two phases 30 a and 30 b are equal, orif the area under each of the phases (their integrals) is equal, as isknown.

Although not shown, the waveforms may also be monophasic, meaning thatthere is only one active phase, i.e., only first phase 30 a or secondphase 30 b.

FIG. 3 shows that stimulation circuitry 28 can include passive recoverycircuitry, which is described further in U.S. Patent ApplicationPublications 2018/0071527 and 2018/0140831. Specifically, passiverecovery switches 41 _(i) may be attached to each of the electrode nodesei 39, and are used to passively recover any charge remaining on theDC-blocking capacitors Ci 38 after issuance of a last pulse phase—i.e.,after the second phase 30 b if a biphasic pulses are used, or after thesole pulse phase if monophasic pulses are used. Passive charge recoverycan be prudent when biphasic pulses are used, because non-idealities inthe stimulation circuitry 28 may lead to phases 30 a and 30 b that arenot perfectly charge balanced. Further, passive charge recovery can benecessary when monophasic pulses are used because there is no equal andopposite active phase to recover the charge.

Passive recovery can occur during at least a portion 30 c of the quietperiods between the waveforms by closing passive recovery switches 41_(i). As shown in FIG. 3, the other end of the switches 41 _(i) notcoupled to the electrode nodes ei 39 are connected to a common referencevoltage, which in this example comprises the voltage of the battery 14,Vbat, although another reference voltage could be used. As explained inthe above-cited references, passive charge recovery tends to equilibratethe charge on the DC-blocking capacitors 38 by placing the capacitors inparallel between the reference voltage (Vbat) and the patient's tissue.Note that passive charge recovery is illustrated as smallexponentially-decaying curves during 30 c in FIG. 2A due to the R-Cnature of the circuit, and this current may be positive or negativedepending on whether phase 30 a or 30 b has a predominance of charge ata given electrode. These exponentially-decaying curves would be largerwere monophasic pulses used.

FIG. 4 shows an external trial stimulation environment that may precedeimplantation of an IPG 10 in a patient. During external trialstimulation, stimulation can be tried on a prospective implant patientwithout going so far as to implant the IPG 10. Instead, one or moretrial electrode arrays 17′ (e.g., one or more trial percutaneous leads15 or trial paddle leads 19) are implanted in the patient's tissue at atarget location 52, such as within the spinal column as explainedearlier. The proximal ends of the trial electrode array(s) 17′ exit anincision 54 and are connected to an External Trial Stimulator (ETS) 50.The ETS 50 generally mimics operation of the IPG 10, and thus canprovide stimulation to the patient's tissue via its stimulationcircuitry 58, which may be equivalent or identical to stimulationcircuitry 28 in the IPG 10. The ETS 50 is generally worn externally bythe patient for a short while (e.g., two weeks), which allows thepatient and his clinician to experiment with different stimulationparameters to hopefully find a stimulation program that alleviates thepatient's symptoms (e.g., pain). If external trial stimulation provessuccessful, the trial electrode array(s) 17′ are explanted, and a fullIPG 10 and a permanent electrode array 17 (e.g., one or morepercutaneous 15 or paddle 19 leads) are implanted as described above; ifunsuccessful, the trial electrode array(s) 17′ are simply explanted.

Like the IPG 10, the ETS 50 can include one or more antennas to enablebi-directional communications with external devices such as those shownin FIG. 5. Such antennas can include a near-field magnetic-inductioncoil antenna 56 a, and/or a far-field RF antenna 56 b, as describedearlier. ETS 50 may also include a battery (not shown) for operationalpower.

FIG. 5 shows various external devices that can wirelessly communicatedata with the IPG 10 and the ETS 50, including a patient hand-heldexternal controller 60, and a clinician programmer 70. Both of devices60 and 70 can be used to wirelessly transmit a stimulation program tothe IPG 10 or ETS 50—that is, to program their stimulation circuitries28 and 58 to produce stimulation with a desired amplitude and timingdescribed earlier. Both devices 60 and 70 may also be used to adjust oneor more stimulation parameters of a stimulation program that the IPG 10or ETS 50 is currently executing. Devices 60 and 70 may also wirelesslyreceive information from the IPG 10 or ETS 50, such as various statusinformation, etc.

External controller 60 can be as described in U.S. Patent ApplicationPublication 2015/0080982 for example, and may comprise a controllerdedicated to work with the IPG 10 or ETS 50. External controller 60 mayalso comprise a general purpose mobile electronics device such as amobile phone which has been programmed with a Medical Device Application(MDA) allowing it to work as a wireless controller for the IPG 10 or ETS50, as described in U.S. Patent Application Publication 2015/0231402.External controller 60 includes a Graphical User Interface (GUI),preferably including means for entering commands (e.g., buttons orselectable graphical icons) and a display 62. The external controller60's GUI enables a patient to adjust stimulation parameters, although itmay have limited functionality when compared to the more-powerfulclinician programmer 70, described shortly.

The external controller 60 can have one or more antennas capable ofcommunicating with the IPG 10 and ETS 50. For example, the externalcontroller 60 can have a near-field magnetic-induction coil antenna 64 acapable of wirelessly communicating with the coil antenna 27 a or 56 ain the IPG 10 or ETS 50. The external controller 60 can also have afar-field RF antenna 64 b capable of wirelessly communicating with theRF antenna 27 b or 56 b in the IPG 10 or ETS 50.

Clinician programmer 70 is described further in U.S. Patent ApplicationPublication 2015/0360038, and can comprise a computing device 72, suchas a desktop, laptop, or notebook computer, a tablet, a mobile smartphone, a Personal Data Assistant (PDA)-type mobile computing device,etc. In FIG. 5, computing device 72 is shown as a laptop computer thatincludes typical computer user interface means such as a screen 74, amouse, a keyboard, speakers, a stylus, a printer, etc., not all of whichare shown for convenience. Also shown in FIG. 5 are accessory devicesfor the clinician programmer 70 that are usually specific to itsoperation as a stimulation controller, such as a communication “wand” 76coupleable to suitable ports on the computing device 72, such as USBports 79 for example.

The antenna used in the clinician programmer 70 to communicate with theIPG 10 or ETS 50 can depend on the type of antennas included in thosedevices. If the patient's IPG 10 or ETS 50 includes a coil antenna 27 aor 56 a, wand 76 can likewise include a coil antenna 80 a to establishnear-field magnetic-induction communications at small distances. In thisinstance, the wand 76 may be affixed in close proximity to the patient,such as by placing the wand 76 in a belt or holster wearable by thepatient and proximate to the patient's IPG 10 or ETS 50. If the IPG 10or ETS 50 includes an RF antenna 27 b or 56 b, the wand 76, thecomputing device 72, or both, can likewise include an RF antenna 80 b toestablish communication with the IPG 10 or ETS 50 at larger distances.The clinician programmer 70 can also communicate with other devices andnetworks, such as the Internet, either wirelessly or via a wired linkprovided at an Ethernet or network port.

To program stimulation programs or parameters for the IPG 10 or ETS 50,the clinician interfaces with a clinician programmer GUI 82 provided onthe display 74 of the computing device 72. As one skilled in the artunderstands, the GUI 82 can be rendered by execution of clinicianprogrammer software 84 stored in the computing device 72, which softwaremay be stored in the device's non-volatile memory 86. Execution of theclinician programmer software 84 in the computing device 72 can befacilitated by controller circuitry 88 such as one or moremicroprocessors, microcomputers, FPGAs, DSPs, other digital logicstructures, etc., which are capable of executing programs in a computingdevice, and which may comprise their own memories. In one example,controller circuitry 88 may comprise an i5 processor manufactured byIntel Corp., as described athttps://www.intel.com/content/www/us/en/products/processors/core/i5-processors.html.Such controller circuitry 88, in addition to executing the clinicianprogrammer software 84 and rendering the GUI 82, can also enablecommunications via antennas 80 a or 80 b to communicate stimulationparameters chosen through the GUI 82 to the patient's IPG 10 or ETS 50.

The GUI of the external controller 60 may provide similar functionalitybecause the external controller 60 can include the same hardware andsoftware programming as the clinician programmer. For example, theexternal controller 60 includes control circuitry 66 similar to thecontroller circuitry 88 in the clinician programmer 70, and maysimilarly be programmed with external controller software stored indevice memory.

SUMMARY

A method is disclosed for configuring an implantable stimulator devicefor a patient using an external device in communication with theimplantable stimulator device, wherein the implantable stimulator devicecomprises an electrode array implanted in the patient. In one example,the method may comprise: (a) providing a plurality of selectable optionsin a user interface of the external device, wherein each selectableoption comprises an anatomical target, wherein each anatomical target isassociated in the external device with a searching pole configurationconfigured to recruit that anatomical target and a measurement; (b)receiving an input at the user interface to select one of the anatomicaltargets; (c) receiving inputs at the user interface to move thesearching pole configuration associated with the selected anatomicaltarget to different searching positions in the electrode array; (d) ateach of the different searching positions, (i) applying the searchingpole configuration associated with the selected anatomical target to thepatient, (ii) performing the measurement associated with the anatomicaltarget, and (iii) storing the searching position and its associatedmeasurement in a memory in the external device; and (e) automaticallydetermining at the external device from the stored plurality ofsearching positions and their associated measurements one or morecandidate positions in the electrode array at which a therapeuticstimulation program can be applied to the patient.

In one example, the measurement is configured to gauge the effectivenessof the searching pole configuration at each of the different searchingpositions. In one example, the measurements associated with theanatomical targets are different for at least some of the anatomicaltargets. In one example, the searching pole configurations associatedwith the anatomical targets are different for at least some of theanatomical targets. In one example, the electrode array is implanted inthe spinal column of the patient. In one example, the measurementcomprises a subjective measurement comprising patient feedback. In oneexample, the subjective measurement comprises patient feedbackconcerning how effectively the searching pole configuration addresses asymptom of the patient or produces sequelae at a dermatomal oranatomical location in the patient. In one example, the measurementcomprises an objective measurement taken from the patient. In oneexample, the objective measurement comprises a neural response of thespinal cord. In one example, the objective measurement is taken by theimplantable stimulator device. In one example, the objective measurementis taken by a device separate from the implantable stimulator device. Inone example, each anatomical target is associated in the user interfacewith its searching pole configuration and its measurement. In oneexample, the one or more candidate positions comprise the searchingpositions where the measurements indicate that the searching poleconfiguration has been effective for the patient. In one example, themethod may further comprising determining a coupling parameter for atleast some or all of the electrodes in the electrode array, wherein eachcoupling parameter is indicative of how well its electrode is coupled tothe spinal cord. In one example, the coupling parameter for at leastsome or all of the electrodes is determined using subjectivemeasurements comprising patient feedback. In one example, the couplingparameter for at least some or all of the electrodes is determined usingobjective measurements taken from the patient. In one example, in step(e) the one or more candidate positions are also determined using thecoupling parameters. In one example, the one or more candidate positionsare determined as those for which a variance of the coupling parametersproximate to the searching positions are low. In one example, in step(d)(i), the applied searching pole configuration is modified at thedifferent searching positions in accordance with the determined couplingparameters. In one example, the method may further, in step (d),determining a paresthesia threshold for the searching pole configurationat each of the different searching positions, and in step (d)(iii)storing the searching position and its associated measurement and itsassociated paresthesia threshold in the memory in the external device.In one example, in step (e), the one or more candidate positions areautomatically determined from the stored plurality of searchingpositions, their associated measurements, and their associatedparesthesia thresholds. In one example, the one or more candidatepositions comprise the searching positions where the measurementsindicate that the searching pole configuration has been effective forthe patient and where the paresthesia thresholds are highest. In oneexample, the method may further comprise determining a couplingparameter for at least some or all of the electrodes in the electrodearray, wherein each coupling parameter is indicative of how well itselectrode is coupled to the spinal cord, and wherein in step (e) the oneor more candidate positions are automatically determined from the storedplurality of searching positions, their associated measurements, theirassociated paresthesia threshold, and the coupling parameters. In oneexample, the searching positions comprise a center of an electricalfield formed by the searching pole configuration.

A method is disclosed for configuring an implantable stimulator devicefor a patient using an external device in communication with theimplantable stimulator device, wherein the implantable stimulator devicecomprises an electrode array implanted in the patient. In one example,the method may comprise: (a) providing a plurality of selectable optionsin a user interface of the external device, wherein each selectableoption comprises a searching pole configuration, wherein each searchingpole configuration is associated in the external device with ameasurement and with a therapeutic stimulation program; (b) receiving aninput at the user interface to select one of the searching poleconfigurations; (c) receiving inputs at the user interface to move theselected searching pole configuration to different searching positionsin the electrode array; (d) at each of the different searchingpositions, (i) applying the searching pole configuration to the patient,(ii) performing the measurement associated with the searching poleconfiguration, and (iii) storing the searching position and itsassociated measurement in a memory in the external device; (e)automatically determining at the external device from the storedplurality of searching positions and their associated measurements oneor more candidate positions in the electrode array; and (f) applying thetherapeutic stimulation program associated with the searching poleconfiguration at a position in the electrode array that is centered withat least one of the one or more candidate positions.

In one example, the measurement is configured to gauge the effectivenessof the searching pole configuration at each of the different searchingpositions. In one example, the measurements associated with thesearching pole configurations are different for at least some of thesearching pole configurations. In one example, the therapeuticstimulation programs associated with the searching pole configurationsare different for at least some of the searching pole configurations. Inone example, the electrode array is implanted in the spinal column ofthe patient. In one example, the measurement comprises a subjectivemeasurement comprising patient feedback. In one example, the subjectivemeasurement comprises patient feedback concerning how effectively thesearching pole configuration addresses a symptom of the patient orproduces sequelae at a dermatomal or anatomical location in the patient.In one example, the measurement comprises an objective measurement takenfrom the patient. In one example, the objective measurement comprises aneural response of the spinal cord. In one example, the objectivemeasurement is taken by the implantable stimulator device. In oneexample, the objective measurement is taken by a device separate fromthe implantable stimulator device. In one example, each searching poleconfiguration is associated in the user interface with its measurementand its therapeutic stimulation program. In one example, the one or morecandidate positions comprise the searching positions where themeasurements indicate that the searching pole configuration has beeneffective for the patient. In one example, the method may furthercomprise determining a coupling parameter for at least some or all ofthe electrodes in the electrode array, wherein each coupling parameteris indicative of how well its electrode is coupled to the spinal cord.In one example, the coupling parameter for at least some or all of theelectrodes is determined using subjective measurements comprisingpatient feedback. In one example, the coupling parameter for at leastsome or all of the electrodes is determined using objective measurementstaken from the patient. In one example, in step (e) the one or morecandidate positions are also determined using the coupling parameters.In one example, the one or more candidate positions are determined asthose for which a variance of the coupling parameters proximate to thesearching positions are low. In one example, in step (d)(i), the appliedsearching pole configuration is modified at the different searchingpositions in accordance with the determined coupling parameters. In oneexample, the method may further comprise, in step (d), determining aparesthesia threshold for the searching pole configuration at each ofthe different searching positions, and in step (d)(iii) storing thesearching position and its associated measurement and its associatedparesthesia threshold in the memory in the external device. In oneexample, in step (e), the one or more candidate positions areautomatically determined from the stored plurality of searchingpositions, their associated measurements, and their associatedparesthesia thresholds. In one example, the one or more candidatepositions comprise the searching positions where the measurementsindicate that the searching pole configuration has been effective forthe patient and where the paresthesia thresholds are highest. In oneexample, the method may further comprise determining a couplingparameter for at least some or all of the electrodes in the electrodearray, wherein each coupling parameter is indicative of how well itselectrode is coupled to the spinal cord, and wherein in step (e) the oneor more candidate positions are automatically determined from the storedplurality of searching positions, their associated measurements, theirassociated paresthesia threshold, and the coupling parameters. In oneexample, the searching positions comprise a center of an electricalfield formed by the searching pole configuration. In one example, theapplied therapeutic stimulation program comprises a therapeutic poleconfiguration that is different from its associated searching poleconfiguration. In one example, the applied therapeutic stimulationprogram comprises a therapeutic pole configuration that is the same asits associated searching pole configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an Implantable Pulse Generator (IPG), in accordance withthe prior art.

FIGS. 2A and 2B show an example of stimulation waveforms producible bythe IPG or in an External Trial Stimulator (ETS), in accordance with theprior art.

FIG. 3 shows stimulation circuitry useable in the IPG or ETS, inaccordance with the prior art.

FIG. 4 shows an ETS environment useable to provide stimulation beforeimplantation of an IPG, in accordance with the prior art.

FIG. 5 shows various external devices capable of communicating with andprogramming stimulation in an IPG and ETS, in accordance with the priorart.

FIG. 6 shows an example of a fitting algorithm operable in a clinicianprogrammer and usable during pole configuration steering to assist indetermining candidate positions in the electrode array for receivingtherapeutic stimulation programs.

FIG. 7 shows a Graphical User Interface operable in the clinicianprogrammer for implementing the fitting algorithm, and shows a step whencoupling parameters are determined for each electrode.

FIGS. 8A and 8B respectively show determination of coupling parametersusing subjective and objective measurements.

FIG. 9 shows a Graphical User Interface operable in the clinicianprogrammer for implementing the fitting algorithm, and shows a stepduring which a pole configuration and/or an associated anatomical targetcan be selected for use during sweet spot searching.

FIGS. 10A-10D shows different examples of selected pole configurationsdesigned to recruit different anatomical targets, or that use differenttypes of measurements to gauge pole configuration effectiveness atdifferent positions in the electrode array.

FIGS. 11A-11C show examples in which a tripole configuration designed torecruit neural targets in the dorsal column is steered to differentposition in the electrode array, and shows recording of differentsubjective measurements of effectiveness at each position, as well as aparesthesia threshold at each position.

FIG. 12 shows an example in which a tripole configuration designed torecruit neural targets in the dorsal column is steered to differentposition in the electrode array, and shows recording of differentobjective measurements of effectiveness at each position, as well as aparesthesia threshold at each position.

FIGS. 13A and 13B shows different manners of evaluating of the storedmeasurements at each position to determine one or more candidatepositions for the application of therapeutic stimulation programs.

FIG. 14 shows application of a therapeutic stimulation program at one ormore of the determined candidate positions.

DETAILED DESCRIPTION

In an SCS application, it is desirable to determine a therapeuticstimulation program that will be effective for each patient. Asignificant part of determining an effective stimulation program is todetermine which electrodes 16 in the electrode array 17 or 17′ should beactive, and with what polarities and relative amplitudes, to recruit andthus treat a neural site at which pain originates in a patient.Selecting electrodes proximate to this neural site of pain can bedifficult to determine, and experimentation is typically undertaken toselect the best combination of electrodes to provide a patient'stherapy.

One method for determining where a site of neural pain may be relativeto the electrode array 17 or 17′, and hence which electrodes should beselected for eventual therapy, is known as “sweet spot” searching. Forexample, and as explained in U.S. Patent Application Publications2019/0046800 and 2019/0366104, sweet spot searching can occur byselecting at the clinician programmer 70 a particular poleconfiguration, and using the clinician programmer to move thatconfiguration around in the electrode array 17 or 17′ while receivingfeedback from the patient as to which position(s) provides symptomatic(e.g., pain) relief. For example, a bipole configuration can be definedusing the clinician programmer 70 at electrodes E1 and E2, with E1comprising the anode and E2 the cathode, with the patient providingfeedback as to how well the bipole at that location “covers” their pain.Thereafter, the bipole can be moved to electrode E2 and E3, with E2comprising the anode and E3 the cathode, and again with the patientproviding feedback at this new bipole location, etc. If the patient'sfeedback suggests that the E4/E5 bipole is best effective, this mayinform the clinician that the site of neural pain is proximate to theseelectrodes, and therefore that a therapeutic stimulation program can bedetermined for use by the patient going forward using these electrodes,or electrodes close to them. Both sweet spot searching and the eventualtherapeutic stimulation program may be supra-perception, meaning thatthe patient can feel the stimulation (e.g., paresthesia), orsub-perception, meaning that the patient cannot feel the stimulation (noparesthesia).

The inventors have recognized that different pole configurations areuseful in targeting different anatomical targets in the spinal cord. Forexample, and as discussed later, a bipole configuration is useful to therecruitment of neural fibers in the dorsal horn of the spinal cord.Because the dorsal horn contains inhibitory interneurons which whenrecruited can inhibit neural conduction, see U.S. Patent ApplicationPublication 2020/0061380, such a bipole configuration is particularlyuseful in providing therapy which is sub-perception. By contrast, aspread monopole configuration is more useful at recruiting neural fibersin the dorsal roots of the spinal cord, which tends to besupra-perception and thus provides paresthesia. Depending on thecircumstances, and perhaps the patient's symptoms, sweet spot searchingmight benefit from use of different types of pole configurationsdesigned to recruit these different anatomical targets.

The inventors have also recognized that gauging the effectiveness ofdifferent pole configurations during sweet spot searching may requiredifferent forms of measurements. For example, the effectiveness of poleconfigurations that are more likely to provide supra-perceptionstimulation may be best gauged subjectively—that is, by having thepatient provide feedback. By contrast, the effectiveness of poleconfigurations that are more likely to provide sub-perceptionstimulation may be best gauged objectively by taking measurements fromthe patient, such as by monitoring neural responses to the appliedstimulation. An example of a neural response that can be used to gaugethe effectiveness of stimulation can include assessment of EvokedCompound Action Potentials (ECAPs), as explained in U.S. PatentApplication Publication 2019/0099602. Having said this, ECAPmeasurements can be used to assess the effects of supra-perceptionstimulation as well, as ECAPs are believed to be caused by dorsal column(DC) activation—the same neural elements that are believed to underlieparesthesia. In any event, the type of pole configuration used (andhence the anatomical target chosen) may warrant the use of differenttypes of measurements during the sweet spot search.

Still further, the inventors have recognized that the effectiveness ofsweet spot searching can be affected by the degree to which theelectrode array is coupled to the spinal cord and other relevant neuraltargets more generally. Given the complex nature of the environment inwhich the electrode array 17 or 17′ is implanted, some electrodes 16 inthe array 17 or 17′ may be closer to relevant neural targets thanothers. This may warrant adjusting the energy (e.g., current) that isprovided to different electrodes in a particular pole configuration toensure the effectiveness of the pole configuration during the sweet spotsearch. For example, poorly coupled electrodes may be provided largercurrents, and well coupled electrodes may be provided smaller currents.Further, an understanding of electrode coupling to neural targets can beuseful in gauging the effectiveness of the sweet spot search and inselecting one or more positions in the electrode array 17 or 17′ towhich an eventual therapeutic stimulation program will be applied.

To address these observations, the inventors have devised a fittingalgorithm 100, which is summarized in flow chart form in FIG. 6. Varioussteps of the fitting algorithm 100 are discussed in detail and shown insubsequent figures. While the fitting algorithm 100 preferably includesall steps described in FIG. 6 for optimal performance, individual steps,or subsets of these steps, are also believed to be inventive in theirown right. In other words, it is not strictly required in all usefulembodiments of the invention that the fitting algorithm 100 includes alldescribed steps.

The fitting algorithm 100 is preferably performed on a newly-implantedpatient, such as a patient who has had a trial electrode array 17′implanted for use with an ETS 50, or a patient who has received afully-implanted IPG 10 and electrode array 17 (FIG. 4). That being said,fitting algorithm 100 could be implemented with a patient at any time,as might be useful to determining or adjusting one or more optimaltherapeutic stimulation programs for the patient. For example, scartissue formation, or migration of the electrode array 17 or 17′ in thepatient, may warrant (re)running the fitting algorithm 100 to adjust apatient's therapeutic stimulation program to one that is more suitablegiven such changes in physiology over time.

As shown in subsequent figures, the fitting algorithm 100 is preferablyimplemented on an external device (e.g., a clinician programmer 70; FIG.5) in communication with the patient's implanted device (IPG 10 or ETS50), and preferably includes a Graphical User Interface (GUI) 120rendered on the external device. Alternatively, the fitting algorithm100 can be implemented on another type of external device, such as thepatient's external controller 60 (FIG. 5). The fitting algorithm 100 cancomprise a portion of the clinician programmer software 84 describedearlier, and executed by the clinician programmer's controller circuitry88 as described earlier. Aspects of the fitting algorithm 100, includingthose necessary to render the GUI 120, can comprise instructions storedon a non-transitory computer-readable medium which the controllercircuitry 88 can read and execute, such as a magnetic, optical, orsolid-state memory. Such memories may be present in the external device(e.g., as memory within or accessible to the controller circuitry 88),or may be loadable into such a device.

In one example, the fitting algorithm 100 in step 102 first determines acoupling parameter (CP) for at least some, and preferably all, of theelectrodes 16 in the electrode array 17 or 17′. Said simply, thecoupling parameters inform how well each electrode is coupled to thespinal cord or other neural targets. As noted earlier, some electrodesmay be closer to the relevant neural targets than others, with closerelectrode being well coupled, and farther electrodes being more poorlycoupled. The coupling parameters for each electrode are determined instep 102 by providing a stimulus, and monitoring a response to thatstimulus. As shown in step 104, such monitoring can be subjective(involving patient feedback) or objective (by measuring a physicalresponse in the patient to the stimulus).

FIG. 7 shows a first example of the GUI 120 rendered on the clinicianprogrammer 70 that can be used to define a stimulus 129 (FIGS. 8A and8B) used to determine the coupling parameters. A leads interface 122shows the electrode array 17 or 17′, i.e., each of the leads, that isimplanted in the patient. In the example shown, two percutaneous leads15 are shown in the leads interface 122, but a paddle lead 19 (FIG. 1)or other type of lead(s) could be used as well. Although not shown, theleads interface 122 can show the relative position of the leads to eachother (e.g., how they are angled or offset from one another), and canshow the relative position of the leads to a patient's anatomicalstructures, such as various vertebrae as determined using fluoroscopicimaging for example. Further, the types of lead(s) that have been usedin the patient can be selected in the GUI 120, thus allowing the fittingalgorithm 100 to understand the relative size of that lead and thespacing of its electrodes in X and Y directions.

GUI 120 preferably also includes interfaces useful to define thestimulus 129 used in determining the coupling parameters. For example,parameters interface 128 can be used to define the basic parameters ofstimulus 129 (FIG. 8A). Preferably, the stimulus 129 comprisesstimulation pulses, similar to those described earlier with reference toFIG. 2A. The parameters interface 128 allows the clinician to adjust forexample pulse amplitude (A), pulse widths (PW; or the pulse widths PWaand PWb of individual phases of the pulses), and frequency (f). Manyother parameters can be included in parameter interface 128 to shape anappropriate stimulus 129, but only these parameters are shown forsimplicity.

A polarity interface 130 can be used to define the polarity of thestimulus 129 at any given electrode, and in this regard, a cursor 124can be used to select various electrodes 16 as shown in the leadsinterface. It is seen in the illustrated example that electrode E8 hasbeen selected to act as a cathode (−), and that the case electrode Ec(12) has been selected to act as an anode (+), in what is known asmonopolar stimulation. Also present in the polarity interface 130 is anoption to specify the amount X % of current—i.e., the fraction of theamplitude A—that is to be provided to each selected electrode. In thisexample, because there is only one cathode (E8) and one anode (Ec),these electrodes will receive 100% of the total current. That is, E8will receive a cathodic current of A*−100%=−A, while Ec will receive ananodic current of A*+100%=+A. As will be shown in different exampleslater, more than one anode electrode and more than one cathode electrodecan be selected, and the anodic and cathodic currents can be shared indifferent proportions by adjusting X in the polarity interface 130.

A waveform phase interface 132 can be used to define the various phasesof the stimulus 129, which may be monophasic or biphasic, as explainedearlier. Further, the use of passive charge recovery can also beprescribed in waveform phase interface 132. Again, only a basic waveformphase interface 132 is shown for simplicity, but it should be understoodthat other options could be presented to allow waveforms with moresophisticated phases, or larger numbers of phases, to be defined for thestimulus 129.

Monitoring interface 104 corresponds to step 104 of FIG. 6, and allowsfor the type of measurement used during coupling parameter determinationto be defined. As noted earlier, such measurement may be subjective,involving patient feedback. In one example, the measurement may involvedetermining a paresthesia threshold at each electrode—e.g., determininga lowest current amplitude A at which stimulation is felt by thepatient, as described later with respect to FIG. 8A. Other subjectivemeasurements could also be used and selected. For example, anothersubject measurement can comprise a lowest amount of total charge (e.g.,A*PW) that can be felt by the patient. Still other subjective measurescan be used. For example, a constant stimulus can be provided at eachelectrode, with the patient providing a subjective ranking (e.g., on ascale of 1 to 10) as to the perceived strength of the stimulus 129.

Monitoring interface 104 may also allow the clinician to select anobjective measurement to be used during coupling parameterdetermination. For example, the clinician can select to monitor ECAPsresulting from the stimulus, as described later with respect to FIG. 8B.Still other neural responses can be monitored, such as Dorsal RootPotentials (DRPs), or other objective measurements discussed later.

FIGS. 8A and 8B respectively show examples in which coupling parametersare determined using subjective and objective measurements. In eachexample, biphasic pulses are used as the stimulus 129, as may beselected in the waveform phase interface 132, although again other typesof waveforms could be used for the stimulus 129 as well (e.g.,monophasic pulses). Although not shown, passive charge recovery may alsobe used after the issuance of both pulse phases as described earlier.Further, in this example, the stimulus is monopolar, and is thuspresented at a single electrode, using the case electrode Ec (12) as areturn path. Again, this isn't necessary, and other types of pulses(e.g., bipolar pulses using two lead based electrodes) could be used forthe stimulus 129 as well, for example by designating desired electrodesas anodes or cathodes using the polarity interface 130.

In FIG. 8A, a paresthesia threshold is used as a subjective measurementto determine the coupling parameter at each electrode. Thus, pulses areprovided first at electrode E1 (and at return electrode Ec). Theamplitude A of the pulse (i.e., the amplitude of either or both of thepulse phases) is gradually increased (using parameter interface 128)until the patient reports perceiving the stimulation. At electrode E1,this paresthesia threshold occurs at an amplitude of 1.0 mA, a valuewhich is stored in a coupling parameter database 125 in the clinicianprogrammer 70's memory. Next, the same pulses are provided to electrodeE2, again with increasing amplitude, until the paresthesia threshold(1.2 mA) is determined at this electrode. It is preferred that otherpulse parameters (e.g., PW, f) remain constant from electrode toelectrode. Note that because the paresthesia threshold is higher (1.2mA) at E2 than for E1 (1.0 mA), electrode E2 can be said to be morepoorly coupled to neural targets than electrode E1, because a highercurrent is needed at E2 to achieve perceptibility. This process repeatspreferably at all other electrodes in the array 17 or 17′ (E3, E4,etc.), until the paresthesia thresholds are populated in the couplingparameter database 125.

In FIG. 8B, a particular feature of detected ECAPs—such as thepeak-to-peak amplitude—is used as an objective measurement to determinethe coupling parameter at each electrode. In this example, pulses areprovided to each electrode, and the resulting amplitude of the ECAP ismeasured. Note in this example that the ECAPs are preferably sensed atelectrodes in the array 17 or 17′ that don't receive the stimulus 129.Thus, when the pulses are provided to electrode E1, E5 (rostral to E1)is used to sense the ECAPs. By contrast, when pulses are provided toelectrode E2, E6 is used to sense the ECAPs. It is desirable to keep thespacing between the stimulating electrode and the sensing electrodeconstant (e.g., a four-electrode distance). This is because ECAPamplitude varies as a function of distance from the stimulatingelectrode, and thus keeping a constant spacing ensures that differencesin ECAP amplitude are solely due to coupling. If necessary, therostral-caudal positioning of the sensing electrode can be changedrelative to the stimulating electrodes. For example, when a most-rostralelectrode E8 is used as the stimulating electrode, a more-caudalelectrode E4 can be used as the sensing electrode.

In the depicted example, amplitude (A) and preferably other parameters(PW, f) of the stimulus 129 are kept constant at each of the testedelectrodes. The detected ECAP amplitude when E1 receives the stimulus129 is 65 microvolts, while the sensed amplitude when E2 is stimulatedis 88 microvolts. This suggests that E2 is better coupled to the neuraltarget than is E1, because stimulation at E2 invokes a larger responsefor the same stimulus amplitude. In any event, once all electrodes aretested, the resulting ECAP amplitudes can be stored in the couplingparameter database 125, similar to what occurred when subjectivemeasurements were taken (FIG. 8A). Note that other features of theresulting neural response can be measured and stored as the couplingparameter at each electrode. For example, and as explained in U.S.Patent Application Publication 2019/0099602, other features of the ECAP(e.g., its area, length, other peak heights, etc.) can also be used asobjective measurements. In another example, the stimulus 129 provided tothe electrodes may not be constant. For example, the stimulus can beadjusted (e.g., its amplitude A) until an ECAP of a certain amplitudethreshold (e.g., 70 microvolts) is detected, with the amplitude of thatstimulus stored as the coupling parameter. Although not shown, note thatcoupling parameters as stored in database 125 may be normalized inmagnitude.

Coupling parameter measurements in steps 102 and 104 can occur in stilldifferent ways, and U.S. Patent Application Publication 2018/0214689,which is incorporated herein by reference, can also be used.

Referring again to FIG. 6, after determining and storing the couplingparameters, the fitting algorithm 100 can next proceed to step 106,which allows the user to select a pole configuration and/or ananatomical target to be used during sweet spot searching. FIG. 9 showsan example of the GUI 120 at this step. Shown is a table 131 thatinforms the clinician of the types of anatomical targets that can berecruited during the sweet spot search; a searching pole configurationsuitable for recruiting that target and that can be moved to differentpositions in the array 17 or 17′; aspects related to how theeffectiveness of the pole configuration can be measured (M) at eachposition during the sweet spot search; and, optionally, a defaulttherapeutic stimulation program that may be used by the clinician afterthe sweet spot searching is completed. All or parts of table 131 can bestored in memory in the clinician programmer 70 so that they may beretrieved and displayed once the GUI 120 has reached step 106 of thefitting algorithm. In the illustrated example, each row is selectable bythe clinician to automatically define the manner in which sweet spotsearching will occur.

Table 131 can be arrived by experimentation or by an understanding ofneural physiology—i.e., by understanding which anatomical targets arebest or most logically recruited by particular pole configurations.Similar experimentation or understanding can be used in table 131 toassociate an anatomical target or pole configuration with a best type ofmeasurement (e.g., subjective or objective), and further with a besttherapeutic stimulation program to be used after sweet spot searching.The data in table 131 may be updated in the clinician programmer 70, andas reflected in GUI 120, from time to time as new correlations arelearned between different anatomical targets, pole configurations,measurement aspects, and default therapeutic stimulation programs.

The point of table 131, and as reflected in GUI 120, is to assist theclinician during the sweet spot search. Table 131 takes much of theguess work out of sweet spot searching in terms of the anatomical targetto be recruited, the pole configuration best suited to recruit thatanatomical target, and the measurements that are best made to gaugeeffectiveness.

In table 131, the default pole configuration to be used during sweetspot searching comprises a pole definition (e.g., a tripole, bipole,spread monopole), and examples of these types of pole definitions areshown in subsequent drawings. Also shown are a default current fractionand position of each pole in the pole configuration. In FIG. 9, thecurrent fractions of each pole are shown as a percentage of totalamplitude A otherwise specified (see FIGS. 10A-10D), with positivepercentages representing a percentage of anodic current, and negativepercentages representing a percentage of cathodic current.

For example, assume a tripole is selected as is useful to recruitingneural targets in the dorsal column, or conversely that the dorsalcolumn is selected thus giving rise to a default tripole configuration(rows 1 and 2). As shown in the table 131 in FIG. 9, two anode poleswill be formed in the electrode array 17 or 17′, with each receiving 50%of the anodic current (+50%*A), and a single cathode pole will be formedwhich will receive 100% of the cathodic current (−100*A). The positionof each pole in the electrode array 17 or 17′ is shown in parenthesesrelative to a center point (0) of the pole configuration. In thisexample, the position comprises an electrode spacing, with positivenumbers showing the position of the pole rostrally relative to thecenter, and with negative numbers showing the position of the polecaudally relative to the center. Assume a tripole is centered atelectrode E3, as shown in FIG. 10A. This places the single cathode pole(−100(0)) at E3. The two anode poles will then be placed at E5 (+50(+2))rostral to E3, and E1 (+50(−2)) caudal to E3. Pole position mayalternatively comprise an absolute measurement (e.g., in millimeters),which is not difficult for the fitting algorithm 100 to handle becausethe spacing of the physical electrodes 16 in an array 17 and 17′ can beeasily known by virtue of the types of lead(s) that have been used forthe patient.

FIG. 10A as just noted shows an example in which dorsal column/tripolehas selected, and centered at E3. The GUI 120 can allow for adjustmentsfrom the default values for the pole configuration provided by table131. For example, the parameters interface 128 can be used to adjustbasic waveform parameters (e.g., A, PW, f). Additionally, the “focus” ofthe tripole can be adjusted, which defines the positions of the anodepoles relative to the central cathode pole. In the example shown, thefocus is again represented by an electrode spacing number (e.g., 2), butcould also be expressed in absolute terms (e.g., as millimeters). Thefocus of the tripole may be adjusted using a focus interface 140, and tothe right in FIG. 10A the focus has been adjusted to 1.5 electrodes,which places the anode poles at positions between E5 and E4, and betweenE2 and E1.

In this regard, note in the disclosed technique that poles in the poleconfiguration do not need to always be positioned at the physicalpositions of the electrodes. When the position of a pole is set in theGUI 120, an electrode configuration algorithm (not shown) in theclinician programmer 70 can compute what physical electrodes should beactive, and with what polarities and current fractions, to best form thepole at the desired position. The reader is assumed familiar with thiselectrode configuration algorithm, and it is described further forexample in U.S. Patent Application Publication 2019/0175915, which isincorporated herein by reference. Thus, the electrode configurationalgorithm in FIG. 10A operates to automatically select the activeelectrodes necessary to position the anode poles at positions betweenthe electrodes. For example, the anode pole between E5 and E4 isprescribed to receive 50% of the anodic current. As a result, theelectrode configuration algorithm activates both of electrodes E4 andE5, but shares the anodic current between them (+25%*A each) to ineffect create a virtual anode pole between E4 and E5. Likewise, theelectrode configuration algorithm would prescribe currents of +25%*A ateach of electrodes E1 and E2 to form the desired +50*A anode pole at theposition between E1 and E2.

Rows 1 and 2 in table 131 prescribe a tripole to recruit the dorsalcolumn, but prescribe different measurements to gauge effectiveness. Inrow 1, subjective measurements are used, as explained later with respectto FIGS. 11A-11C. In row 2, objective measurements are used,specifically a feature of ECAPs (e.g., amplitude, although otherfeatures can also be used as explained above) that result from the poleconfiguration, as explained later with reference to FIG. 12. In thisobjective measurement example, table 131 preferably automaticallydefines the sense electrode(s) that are to be used in sensing the ECAPamplitude. Again, these sense electrodes are denoted by an electrodespacing relative to the center of the tripole, but again could comprisean absolute measurement. Thus, when sensing ECAPs in this example, oneor more of electrodes spaced rostrally from the center (+5, +6) can beused, and one or more electrodes spaced caudally (e.g., −4) can be used.This is shown in FIG. 10B, where it is assumed that the tripole (i.e.,the cathode pole) is centered at E6. The anode poles in this exampleappear at E8 (+2) and E4 (−2). Sensing electrode S3 appears at E12 (+6relative to center E6), sensing electrodes S2 appears at E11 (+5), andsensing electrode S1 appears at E2 (−4). Note that as the tripole as issubsequently moved, some sensing electrodes will be inaccessible. Forexample, if the center of the tripole is moved to E3, there will be noroom to accommodate sensing electrode S1. Should this occur, othersensing electrodes that can be accommodated may be used (S2 and S3), orthe rostral-caudal nature of the sensing electrodes can be changed(e.g., S1 can be changed from −4 to +4). Note that table 131 couldprescribe that sensing occur using one or more electrodes on a differentlead in the array 17 or 17′ as well (not shown).

Rows 3-4 in table 131 prescribe a spread monopole known to be effectivein recruiting the dorsal roots of the spinal cord. This spread monopoleis shown in FIG. 10C. In this example, the spread monopole comprises aspread cathode, with the cathodic current fractionalized between fivedifferent adjacent electrodes in the array 17 or 17′, with the centralcathode pole receiving 20% of the cathodic current (−20%*A), nextadjacent cathode poles receiving 4% (−4%*A), and still next adjacentcathode poles receiving (−36%*−A), for a total of −100*A. The caseelectrode Ec (12) acts as a return, and thus receives 100% of the anodiccurrent (+100%*A). This spread monopole provides a larger electric fieldin the tissue as is useful for the recruitment of dorsal roots. Notethat a spread interface 141 can be used to adjust the spacing of thepoles in the spread monopole, which by default is set to an electrodespacing of 4.

Rows 3-4 are each associated with different types of measurements thatwill be used during sweet spot searching to gauge the effectiveness ofthe spread monopole. In rows 3 and 4, subjective measurements are usedreliant on patient feedback. In row 3, the patient will provide inputregarding paresthesia, whether stimulation can be felt, or how stronglythe stimulation feels. In row 4, the patient will provide inputregarding proprioception, i.e., how or where the patient sensesstimulation.

In row 5 of table 131, a wider-spread monopole (with a spread of 12) isprescribed, again as useful to recruiting the dorsal roots of the spinalcord. However, in this example, effectiveness is gauged objectively bydetecting the amplitude or other feature of dorsal root potentials(DRPs). In this example, shown in FIG. 10D, sensing of the DRPs canoccur differentially using pairs of electrodes (Si+, Si−), using forexample first and second rostral electrodes from the center of thespread monopole (S1+, S1−), or fourth and fifth rostral electrodes (S2+,S2−), etc.

Rows 6 and 7 target still different neural structures using differentpole configurations, and further illustrate that effectiveness can beobjectively measured using devices external to the IPG or ETS—that is,without sensing a neural response at the electrodes of those devices.For example, in row 6, a spread bipole is used to gauge an overalleffect not particular to any specific neural target, and uses anElectroencephalogram (EEG) on the scalp to gauge effectiveness. Thespread bipole produces a strong but generally uniform electric fieldalong the axis of the bipole (e.g., rostrocaudally), and is usefulbecause certain neural elements in the spinal cord, such as inhibitoryinterneurons and descending terminals, are oriented rostrocaudally and“end” segmentally. Ends that point rostrocaudally are sensitive touniform and strong parallel fields, while axons of passage (such as thedorsal columns) are not sensitive to these fields and are therefore“bypassed” by the stimulation. EEG can be a useful measure ofeffectiveness here because the effects of stimulation (beyondpotentially pain relief) due to sub-perception therapy may not beimmediately felt by the patient, as the spread bipole wouldtheoretically not activate dorsal column fibers responsible forgenerating sensations and paresthesia. In row 7, a bipole is used totarget the dorsal horn and ventral roots, and uses Electromyography(EMG) sensing at a patient's right and left legs to gauge effectiveness.

Although not shown in FIG. 9, table 131 can include further informationabout the directionality of the pole configuration, and/or itsmeasurement, as can be effected using leads having directionalcharacteristics, such as split ring electrodes. See, e.g., U.S. PatentApplication Publication 2020/0001091 (describing the production ofdirectional electric fields in tissue using split-ring electrodes).Options having directionality aspects may not be displayed in table 131if electrodes lacking directionality are used with the patient. Further,it should be understood generally that the selectable rows in table 131can depend, and can be automatically populated, as a function of thetype of leads used (e.g., the number of electrodes, whether theelectrodes are split ring), the type of IPG 10 or ETS 50 used (e.g., dothey support measuring of neural responses such as ECAPs and DRPs), andthe type of measurement equipment (e.g., EEG, EMG, etc.) supported byuse with the system. In other words, these factors may automaticallylimit the options presented in table 131.

Once step 106 has been completed, and a searching poleconfiguration/anatomical target selected, fitting algorithm 100 canproceed to step 108, where the pole configuration is steered todifferent positions in the electrode array 17 or 17′. As shown in FIG.6, this can involve modifying the pole configuration using the couplingparameters determined earlier in step 102 (110); measuring theeffectiveness (M) of the pole configuration at each position (112); anddetermining a paresthesia threshold (PT) at each position (114).

FIGS. 11A-11C show a first example of pole configuration steering 108,which assumes that the clinician has earlier selected from table 131(FIG. 9) to use a tripole during steering to recruit the dorsal columnas an anatomical target. Further, it is assumed in this example that theclinician has selected row 1 in the table 131, and therefore that themeasurements (M) taken during steering involve a subjective measurementfrom the patient. In this example, the measurements include a pain scoreprovided by the patient, although other subjective measurements couldalso be used. Subjective measurements need not necessarily relate to howwell the searching pole configuration addresses a symptom of thepatient. For example, subject measurements can also indicate how well orto what extent the searching pole configuration produces sequelae at adermatomal or anatomical location in the patient.

FIG. 11A shows the selected tripole at a first position (position 1).Pole configuration position can be denoted in different manners, but inone example the position may comprise a point in the array 17 or 17′that comprises a central point of stimulation (CPS) of the poleconfiguration, for example a center point of the electric field createdin the tissue. In the example of a tripole, this central point cancomprise the position of the sole cathode, and so in FIG. 11A, thetripole's position can be said to be at electrode E3. More generally,and because the electrode array 17 and 17′ can be two dimensional—suchas if more than one percutaneous lead is used, or if a paddle lead isused—the CPS can comprise a X,Y coordinate. At position 1, the CPS isX₁,Y₁, which again comprises the center of electrode E3. Different poleconfigurations would have different CPSs. For example, a bipole wouldhave a CPS between the anode and cathode poles, etc. The center point ofthe electric field can be determined in different ways. It can forexample comprise a geometric center, a point at which the electric fieldis the strongest (maximum dV/dt), a point at which its rate is changingthe fastest (maximum d²V/dx²), or other significant points of theelectric field.

At each position, and in accordance with step 110 (FIG. 6), the poleconfiguration is preferably modified in accordance with the electrodecoupling parameters determined earlier in step 102. This step 110 isoptional, but is preferred to “normalize” the effect of the poleconfiguration at each position. Modification of the pole configurationis shown at the bottom of FIG. 11A, and involves scaling the defaultcurrent fractions specified in table 131 (FIG. 9). For example, FIG. 11Ainvolves use of a tripole with a default +50/−100/+50 currentfractionalization, as described earlier. At position 1, electrodes E1,E3, and E5 are involved in forming the poles in the pole configuration.The coupling parameters for these electrodes—as stored in database 125(FIG. 8A) for example, which are representative of a paresthesiathreshold—are 1.0, 1.1, and 1.2 respectively. (Again, objectivemeasurements such as shown in FIG. 8B could also have been used). Assuch, the default current fractions can be changed at these electrodesduring step 110. Anode pole E5 has a higher coupling parameter thananode pole E1, meaning that E5 is more poorly coupled to the spinal cordthan is E1. Step 110 can therefore automatically increase the currentfraction at electrode E5 relative to E1 to compensate for thedifference. For example, the anodic currents at E5 and E1 can beweighted in accordance with their coupling parameters: the couplingparameters at these electrodes can be added (2.2), with E5 adjusted toreceive an anodic current of +55% in accordance with its couplingparameter (e.g., 1.2/2.2), and with E1 adjusted to receive an anodiccurrent of +45% (e.g., 1.0/2.2). This is just one example of how thecurrent fractions for the steering pole configuration from table 131 canbe modified in light of the coupling parameters at each electrode, andother mathematical means of adjustment are possible.

Once the pole configuration is adjusted (110) to account for differencein the electrode coupling parameters, the adjusted pole configuration istransmitted to the IPG or ETS to be applied to the patient, and one ormore measurements (M) of the effectiveness of the pole configuration atthis position can be recorded and stored in the system (step 112; FIG.6). In this example, a subjective measurement is obtained from thepatient, such as a pain score rated on a scale of 1 to 10 (with 10comprising the least pain, and 1 the highest). Other subjectivemeasurements are possible. For example, the patient can be asked todescribe a percentage to which the pole configuration at position 1seems to be covering his pain. The measurements may also be inverted,with lower scores indicating a better patient result. In any event, onceobtained from the patient, the subjective patient score measurement (M)can be entered by the clinician in the GUI 120 as shown. Although notshown, note that there can be more than one subject measurements made instep 112. Multiple measurements at each position can be averaged,weighted and summed, or a best measurement chosen, to arrive at a singlemeasurement. Alternatively, each measurement can be independentlytracked and evaluated, as described later.

At step 114 (FIG. 6), it is preferable (but not strictly necessary) toalso determine a paresthesia threshold (PT) of the pole configuration ateach position, and to record this paresthesia threshold in the GUI 120for storage and later consideration. This paresthesia threshold PTcomprises a lowest level at which the patient can feel stimulation asprovided by the entirety of the entire pole configuration, which againmay comprise a current level. Note that the paresthesia threshold PTdetermination at this step is gauged using the entire poleconfiguration, and as such is different from determination of theper-electrode coupling parameter (CP) described earlier (step 102)(which can also be determined using a paresthesia threshold; e.g., FIG.8A). When determining the paresthesia threshold PT of the poleconfiguration, the clinician may vary the total amplitude A in the GUI120, for example at parameters interface 128, which will vary thecurrent provided to the various poles in the pole configuration inaccordance with their current fractions. As described later withreference to FIGS. 13A and 13B, the paresthesia thresholds PT are usefulto determining candidate positions at which actual therapeuticstimulation programs can be applied to the patient once sweet spotsearching has finished.

As shown, the GUI 120 can include an option to mark the present positionof the pole configuration as one at which a measurement M andparesthesia threshold PT will be taken and stored. This is useful, as itcan allow the clinician to experimentally move the pole configuration todifferent positions (as described below) without necessarily orautomatically recording a measurement and paresthesia threshold at everynew position; some pole configurations positions may not provide usefuldata, or have such a poor patient measurement M that they are not worthrecording.

After recording at least one measurement M of pole configurationeffectiveness at position 1, and preferably also recording theparesthesia threshold PT at that position, the pole configuration can bemoved (steered) to a new location in the electrode array 17 or 17′.Moving of the pole configuration to a new position can be effected usingthe GUI 120 provided by the clinician programmer 70. For example, asshown in FIG. 11A, a position interface 133 can be used to move the poleconfiguration in X or Y positions within the array 17 or 17′.Alternatively, the clinician programmer 70 can include other userinterface elements. For example, the clinician programmer 70 can includea joystick (not shown) or other attachment to the clinician programmerto allow the position of the pole configuration to be moved in thearray. Preferably, the position of the poles as moved is shown on adepiction of the electrode array 17 or 17′ so that they can beunderstood in context.

FIG. 11B shows that the tripole configuration has been moved to a newposition (position 2) which is up rostrally by one electrode, such thatthe tripole (its cathode pole) is now centered at X₂,Y₂ (e.g., E4), withthe anode poles at electrodes E6 and E2. As before the poleconfiguration can be modified (110) to compensate for the couplingparameters (CP) at the electrodes used in forming the poles. Becauseanode pole E6 is better coupled than anode pole E2, the current fractionprovided to E2 can be increased (+55) relative to E6 (+45). In anotheralternative, because the single cathode pole E4 is better coupled thanthe average of the anode poles E2 and E6, part of the cathodic currentcan be moved from the cathode pole E4 (−95) to the case electrode Ec(−5). Again, mathematical weighting can be used to determine how tomodify the pole configuration using the coupling parameters (110). Oncethe modified pole configuration is applied at position 2 (and uponmarking this position if necessary), its position (X₂,Y₂), the relevantpatient measurement M, and the paresthesia threshold PT can be recorded,and the pole configuration then moved (133) to a different position.

FIG. 11C shows the tripole moved to a third position (position 3), andis interesting because in this circumstance the poles in the tripole donot correspond to the physical positions of the electrodes. As notedearlier, an electrode configuration algorithm can be used to computewhat physical electrodes will be active, and with what polarities andcurrent fractions, to best form the poles at the desired position. Inthis example, the electrode configuration algorithm has determined thatelectrodes E1, E2, E3, E4, E5, E9, E11, and E13 should be active, andwith current fractions +35, +5, −75, +5, +35, +10, −25, +10 respectivelyto position the poles of the prescribed +50/−100/+50 tripole at thedesired positions. Thereafter, this default current fractionalizationmay again be modified (110) based on the coupling parameters 125 to anew fractionalization at these electrodes. At this new position (X₃,Y₃),a new patient measurement M and paresthesia threshold PT can bedetermined and stored, and so on for other positions.

FIG. 12 shows another example pole configuration steering 108, whichagain assumes that the clinician has earlier selected from table 131(FIG. 9) to use a tripole during steering to recruit the dorsal columnas an anatomical target. Further, it is assumed in the example that theclinician has selected row 2 in the table 131, and therefore thatobjective measurements (M) will be taken from the patient duringsteering. Specifically, the measurements comprise monitoring an ECAPfeature, such as amplitude, although again other objective measurescould be assessed.

This fitting algorithm 100 process is otherwise similar. The poleconfiguration can be modified using the stored coupling parameters(110). In this example, ECAP amplitudes (FIG. 8B) are used as thecoupling parameters CP for each electrode, but subjectively-determinedcoupling parameters could also have been used (FIG. 8A) to modify thepole configuration. One or more objective measurements are taken (112),and as prescribed by table 131, such measurements are taken at one ormore of electrodes E2 (S1), E11 (S2), and E12 (S3), which will varybased on the current position of the tripole. Selecting to mark thisposition can inform the clinician programmer 70 to wirelessly instructthe IPG 10 or ETS 50 to take the necessary measurements at the necessaryelectrodes, and to wirelessly transmit the measurements back to theclinician programmer 70 for storage. Alternatively, the IPG 10 or ETS 50can provide the clinician programmer 70 data indicative of themeasurement (e.g., the sampled waveform of the ECAPs), with theclinician programmer then analyzing the data to extract the measurement(the ECAP amplitude). Again, the paresthesia threshold PT of the tripoleis taken by adjusting the amplitude A (114) to a lowest level at whichthe patient can feel stimulation as provided by the pole configuration.After recording such measurement(s) and the paresthesia threshold at thefirst position, the pole configuration can then steered to a newlocation (133) and the process repeated.

After the pole configuration has been steered and measurements taken,fitting algorithm 100 can proceed to evaluate the stored data at eachposition to select one or more candidate positions Z_(N) at whicheventual therapy can be applied (116, FIG. 6). An example of thisevaluation step 116 is shown in FIG. 13A. A table 142 shows relevantdata taken and stored in the clinician programmer 70 at each poleconfiguration position (X_(N),Y_(N)) during steering, including the oneor more measurements (M_(N)) taken at that position and the paresthesiathreshold (PT_(N)) of the pole configuration at that position. This datais graphed 144 in FIG. 13A in two dimensions X and Y covering the spanof the electrode array 17 or 17′. Graphing eases understanding of theevaluation of the results, and graph 144 may be displayed in GUI 120,although this isn't strictly necessary. In this example, it is assumedthat higher values for M correspond to better patient results, but thisisn't strictly necessary, because, depending on the nature of themeasurement, lower values for M may indicate better patient results.

It is also assumed that higher values for the paresthesia threshold PTof the pole configurations are a preferred result, but again thisdepends on the manner in which the paresthesia threshold is quantified.In this example, when the paresthesia threshold comprises a lowestcurrent felt by the patient, a higher value is deemed better. This isbecause an eventual therapy stimulation program, if placed at thisposition, should have more headroom or range for current adjustment andbe less sensitive to changes such as electrode movement due to posturalchanges, migration of the electrodes in the spinal column over time,scar tissue formation, etc. If the paresthesia threshold PT is lower,there is less room for current adjustment, especially if sub-perceptiontherapy is to be used. Further, a lower paresthesia threshold PT runs agreater risk of subjecting the patient to excessive therapeutic currentsif changes occur. This can be a concern for example if the patient'sposture changes in a manner that brings the electrode array closer torelevant neural structures. If the paresthesia threshold is low, theprescribed therapeutic current may suddenly be too high for the patient,which may be uncomfortable. Stated simply, a position with a higherparesthesia threshold PT allows for more freedom is choosing therapeuticcurrents, and is less sensitive to postural changes and other patientand/or electrode movements.

Accordingly, in this example and in graph 144, possible candidatepositions Z_(N) for therapy correspond to positions 146 where both themeasurements M and the paresthesia thresholds PT are both high, whichinclude positions X₄,X₄ (Z₄), X₅,Y₅ (Z₅), X₁₂,Y₁₂ (Z₁₂), and X₁₃,Y₁₃(Z₁₃). In this regard, thresholds T(M) and T(PT) can be used todetermine whether the measurement M and paresthesia threshold PT aresuitable for use as a candidate position Z_(N), and it can be see thatboth exceed these thresholds at Z₄, Z₅, Z₁₂, and Z₁₃. Determination ofcandidate positions Z_(N) preferably occur automatically in the fittingalgorithm 100 with reference to thresholds or in accordance with othercomputational techniques described subsequently.

Determining candidate positions Z_(N) for therapy can involve theconsideration of other factors as well. For example, and as shown inTable 142, the variance of the coupling parameters CP proximate to theelectrodes used to create the pole configurations at each position, ormore simply just the electrodes used to create the pole configurationsat each position, can be assessed (see 118, FIG. 9). By way of review,these coupling parameters were determined earlier in steps 102 and 104and stored in database 125 (see FIGS. 8A and 8B). Generally speaking, itis preferred that variance of the electrode coupling parameters near acandidate position be low. This is because as mentioned earlier theelectrode array 17 or 17′ can migrate in a patient over time or as thepatient moves. Low variance also implies a “uniform” spinal cordphysiology (e.g., no unusual tissue features, scarring, dimples orridges in the CSF thickness, etc.) proximate to the position. If thevariance is high, the therapy stimulation program might be moresensitive, and require more frequent adjustment.

One example of determining coupling parameter variance and implementablein the clinician programmer 70 as an algorithm 148 is shown at thebottom of FIG. 13A. The variance algorithm 148 can determine whichelectrodes are generally proximate to the central point of stimulation(CPS) of the pole position at a given measured position. The may includeall electrodes that are a certain distance from the CPS, or perhaps justthe electrodes used to produce the pole configuration. The couplingparameters CP for those electrodes are retrieved, i.e., from database125 (FIGS. 8A and 8B). Then, a measure of variance is determined for theretrieved coupling parameters. In a simple example, this can comprisecomputing a standard deviation of the coupling parameters, althoughother statistical means can be used to determine variance. In anotherexample, the variance may simply comprise the spread or range of theretrieved coupling parameter values. Once the variance of the couplingparameters is determined at each of the positions (VARCP), this variancecan be included and stored in table 142 are shown. Although thisvariance VARCP is not graphed in FIG. 13A, it could be, and further athreshold (T(VARCP)) could be established, with variances below thisthreshold being deemed suitable in the identification of candidatepositions Z_(N).

FIG. 13B shows another algorithm that the clinician program can use atstep 116 to identify candidate positions Z_(N) for the later applicationof therapeutic stimulation programs. In this example, the algorithmcomprises a flow chart which can be run on each position (e.g., each rowin table 142). As a first step, the algorithm determines if a positionhas a good (e.g., high) or poor (e.g., low) patient measurement M, whichcan be assessed using the measurement threshold T(M) discussed earlier.The algorithm then looks at the paresthesia threshold PT at thisposition to determine if it is good (e.g., high) or poor (low), whichcan be assessed using threshold T(PT) discussed earlier. If both themeasurement M and paresthesia threshold PT are good, that position isaccepted as a candidate position Z_(N) for the application of atherapeutic stimulation program. If both the measurement M andparesthesia threshold PT are poor, that position is rejected as acandidate position.

If one of the measurement M or paresthesia threshold PT is good but theother is poor, the positions may possibly be candidate position, and thealgorithm may investigate further by optionally reviewing (step 118,FIG. 6) the variance of the coupling parameters, VARCP, as discussedwith respect to FIG. 13A. If the variance is low, such as determinedwith reference to a variance threshold T(VARCP), the possible candidateposition is accepted as a candidate position ZN; if high, the possiblecandidate position is rejected.

Determination of candidate positions Z_(N) can occur in other ways. Forexample, and as shown in FIG. 13B, one or more equations can be used todetermine a candidate position metric J_(N). Generally speaking, whethera pole configuration position can act as a candidate position Z_(N)depends on the measurement M_(N), the paresthesia threshold PT_(N), andoptionally the coupling parameter variance VARCP_(N) taken at each poleconfiguration position X_(N),Y_(N), and these values can be processed invarious ways to compute a candidate position metric J_(N) for eachposition. For example, M_(N), PT_(N) and VARCP_(N) can be multiplied byweighting factors A, B and C respectively, and then added or subtractedto compute the candidate position metric J_(N) at each position. Inanother example shown, the current fraction percentage at each of theelectrodes used to create the pole configuration can be divided by itscoupling parameter, with these ratios summed and multiplied by aweighting factor C if necessary. In any event, by processing the valuesfrom table 146, a candidate position metric J_(N) can be calculatedindicative of the goodness or the poorness of the pole configuration atthat position. The best candidate position metrics J_(N) (e.g., thethree highest or lowest, depending on the manner in which the metric iscalculated) or those above or below a J_(N) threshold might for examplebe considered as candidate solutions Zn.

The GUI 120 may contain aspects to allow the clinician to control thecandidate position determination to some degree, and a candidateposition interface 151 is shown in FIG. 13B. Generally speaking, thecandidate position interface 151 allows various factors useable todetermine candidate positions Z_(N) to be adjusted, and so can affectthe number of candidate positions that the algorithm might suggest. Forexample, sliders can be used to adjust the measurement threshold T(M)and the paresthesia threshold T(PT) to higher or lower values. If highermeasurements M and paresthesia threshold PT are beneficial to thepatient, increasing either or both of these thresholds will reduce thenumber of possible candidate solutions Z_(N) that the algorithm 116determines, while decreasing either or both will increase the number ofpossible candidate solutions that the algorithm 116 determines. A slidermay also be used to adjust the coupling parameter variance thresholdT(VARCP), which would alter the determination of candidate positions inthe flow chart of FIG. 13B (118). Sliders may also be used to adjust theweights A, B, and C that might be used in the computation of a candidateposition metric J_(N), which again could change the suggest candidatepositions Z_(N). Finally, a generic slider can be used to broaden ornarrow the number of candidate positions Z_(N) output by the algorithm,which may change one or more of the thresholds or weights justdiscussed.

Once one or more candidate positions Z_(N) have been chosen, fittingalgorithm 100 can proceed to step 119 (FIG. 6), where a therapeuticstimulation program can be chosen for the patient that is centered atone of the candidate positions. FIG. 14 shows an example of the GUI 120at this step 119. As shown to the left, the candidate positions Z_(N)determined earlier as being successful positions at which to trytherapeutic stimulation programs can be shown overlaid on the electrodearray 17 or 17′, and in this example it is assumed that four candidatepositions Z₄ (X₄,X₄), Z₅ (X₅,Y₅), Z₁₂ (X₁₂,Y₁₂), and Z₁₃ (X₁₃,Y₁₃) havebeen determined.

The clinician may now select any of these candidate positions (e.g., Z₄)using cursor 124 for example, and devise a therapeutic stimulationprogram that is centered at that position. The clinician could do thismanually. For example, the clinician could select for example to try abipole (132) centered at this position as shown. Notice that the anode(+) and cathode (−) poles of the bipole are equally spaced from, andthus center, candidate position Z₄. Once this bipole has beenpositioned, it can thereafter be modified as necessary to create thetherapeutic stimulation program. For example, the positions of the polescan be varied with respect to the center Z₄, such as by using the focusinterface 140. Further adjustments to arrive at the therapeuticstimulation program can include varying the parameters in parameterinterface 128 (A, PW, f). Note that the therapeutic stimulation programeventually used for the patient's therapy need not be different from thepole configuration used during sweet spot searching (108, FIG. 6). Forexample, if a spread monopole was used during sweet spot searching, itcould again be used as the therapeutic stimulation programs.

Note that the clinician may wish to try therapeutic stimulation programsat one, more, or all of the candidate solutions, to try and determineone or more therapeutic stimulation programs that work best for thepatient. Still, while some degree of experimentation may be warranted atstep 119 to determine one or more therapeutic stimulation programs, useof the fitting algorithm 100 greatly assists the clinician andconveniences the patient, because the candidate solutions narrow thepossible positions at which therapeutic stimulation should be placed.

Interface 150 may also allow the clinician to choose a defaulttherapeutic stimulation program (SP1) centered at one of the candidatepositions Z_(N). This default therapeutic stimulation program maycomprise one associated with the steering pole configuration, anatomicaltarget, and measurement technique that was selected earlier (table 131,FIG. 9). For example, if row 1 was selected in table 131, a defaultstimulation program SP1 may be populated in interface 150.Alternatively, and although not shown, each row in table 131 may beassociated with a number of default therapeutic stimulation programs,each of which can then be populated in interface 150 for selection bythe clinician. Although not shown, interface 150 may include certaininformation about the one of more default therapeutic stimulationprograms, such as their basic parameters (e.g., A, PW, f), its poleconfiguration or other details or descriptors of clinician significance.

Certain default therapeutic stimulation programs associated in table 131can be logically structured in light of the anatomical targets deemed tobe of interest during sweet spot searching. For example, if the dorsalcolumn was the target of interest during sweet spot searching based on apatient's symptoms, it may also be of interest when the therapeuticstimulation programs is used, even if a different pole configuration isused. For example, and as shown in FIG. 15, a more-focused bipoleconfiguration may be used for therapy, even though a tripoleconfiguration was used during sweet spot searching. It may be ideal inthis circumstance that the therapeutic stimulation program besub-perception, even though paresthesia was used during the sweet spotsearch. In this case, the default therapeutic stimulation program mayhave a low amplitude A, or may have a high frequency (e.g., >1 kHz),because there is some evidence to suggest that high frequencystimulation is useful to providing sub-perception therapy. In anotherexample, while it was useful to target a particular anatomical targetduring sweet spot searching, the default stimulation program may bedesigned to target a different anatomical target.

While it is preferred that the therapeutic stimulation program becentered at the candidate positions, it should be understood that suchcentering may not be exactly perfect. System limitations may preventsuch perfect centering. For example, while an electrode configurationalgorithm can be used to activate certain electrodes to approximate thedesired positions of poles in an electrode array, such approximationsare not perfect. As a result, the central point of stimulation of asteering pole configuration determined as a candidate position may notexactly match the central point of stimulation of a pole configurationused in a therapeutic stimulation program. It should therefore beunderstood in context that determined candidate positions and thecentral point of stimulation of therapeutic stimulation programs can besaid to be “centered” if they vary by 3 mm or less.

While disclosed in the context of a spinal cord stimulation system, itshould be understood that the disclosed fitting algorithm can beemployed in other neurostimulation systems. As used herein, the “spinalcord” should be understood as comprising all the neural structureswithin the gray and white matter of the spinal column as well as neuralstructures that branch into or out of the spinal cord, such as thedorsal and ventral columns, the dorsal and ventral horns, the dorsal andventral roots, the dorsal root ganglion, other spinal nerves, etc.

Although particular embodiments of the present invention have been shownand described, it should be understood that the above discussion is notintended to limit the present invention to these embodiments. It will beobvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present invention. Thus, the present invention is intended to coveralternatives, modifications, and equivalents that may fall within thespirit and scope of the present invention as defined by the claims.

What is claimed is:
 1. A method for configuring an implantablestimulator device for a patient using an external system incommunication with the implantable stimulator device, wherein theimplantable stimulator device comprises an electrode array implanted inthe patient, the method comprising: (a) providing a plurality ofselectable options in a user interface of the external system, whereineach selectable option comprises an anatomical target, wherein eachanatomical target is associated in the external system with a poleconfiguration configured to recruit that anatomical target; (b)receiving an input at the user interface to select one of the anatomicaltargets; and (c) applying the pole configuration associated with theselected anatomical target at a position in the electrode array.
 2. Themethod of claim 1, wherein each pole configurations comprise a positionof one or more poles and a current fraction for each one or more poles.3. The method of claim 1, wherein the pole configurations associatedwith the anatomical targets are different for at least some of theanatomical targets.
 4. The method of claim 1, wherein the poleconfigurations associated with the anatomical targets are different forall of the anatomical targets.
 5. The method of claim 1, wherein theelectrode array is implanted in a spinal column of the patient, whereineach anatomical target comprises a different structure in a spinal cordof the patient.
 6. The method of claim 1, wherein each selectable optionis further associated in the external system with a measurement, whereineach measurement is configured to gauge the effectiveness of itsassociated pole configuration.
 7. The method of claim 6, wherein themeasurements associated with the anatomical targets are different for atleast some of the anatomical targets.
 8. The method of claim 6, whereinat least one of the measurements comprises a subjective measurementcomprising patient feedback.
 9. The method of claim 8, wherein thesubjective measurement comprises patient feedback concerning howeffectively the searching pole configuration addresses a symptom of thepatient or produces sequelae at a dermatomal or anatomical location inthe patient.
 10. The method of claim 6, wherein at least one of themeasurements comprises an objective measurement taken from the patient.11. The method of claim 10, wherein the objective measurement is takenby the implantable stimulator device.
 12. The method of claim 1, whereinthe user interface of the external system displays each selectableoption including its anatomical target and its associated poleconfiguration.
 13. The method of claim 1, further comprising (d)receiving inputs at the user interface to move the pole configurationassociated with the selected anatomical target to different positions inthe electrode array.
 14. The method of claim 1, wherein each selectableoption is further associated in the external system with a stimulationprogram.
 15. The method of claim 14, wherein the pole configuration isapplied at the position in the electrode array in accordance with thestimulation program associated with the selected anatomical target. 16.The method of claim 1, further comprising, in step (c), determining aparesthesia threshold for the applied pole configuration, and storingthe paresthesia threshold in a memory in the external device.
 17. Anexternal system for configuring an implantable stimulator device,wherein the implantable stimulator device comprises an electrode arrayimplantable in the patient, the external system comprising: a userinterface configured to provide a plurality of selectable options,wherein each selectable option comprises an anatomical target, whereineach anatomical target is associated in the external system with a poleconfiguration configured to recruit that anatomical target, wherein theuser interface is configured to receive an input at the user interfaceto select one of the anatomical targets, and wherein the external systemis configured to apply the pole configuration associated with theselected anatomical target at a position in the electrode array.
 18. Theexternal system of claim 17, wherein each pole configurations comprise aposition of one or more poles and a current fraction for each one ormore poles.
 19. The external system of claim 17, wherein the poleconfigurations associated with the anatomical targets are different forat least some of the anatomical targets.
 20. A non-transitory computerreadable comprising instructions, wherein the instructions areconfigured to be executed on an external system in communication with animplantable stimulator device, wherein the instructions when executedare configured to: (a) provide a plurality of selectable options in auser interface of the external system, wherein each selectable optioncomprises an anatomical target, wherein each anatomical target isassociated in the external system with a pole configuration configuredto recruit that anatomical target; (b) receive an input at the userinterface to select one of the anatomical targets; and (c) apply thepole configuration associated with the selected anatomical target at aposition in the electrode array.